Lapis Lazuli from the Coquimbo Region, Chile

Abstract

GEMS & GEMOLOGY Spring 2000 apis lazuli is a rock composed of lazurite—the source of the blue color—with variable amounts of other minerals depending on its origin and, typically, small particles of pyrite. Prized for its attractive blue color, lapis lazuli was used in jewelry by some of the world’s most ancient civilizations. The stone is mined at relatively few locations, some of which have been worked since the fifth millennium BC (von Rosen, 1990). Considering the extensive history and romance attached to this ornamental gem material, the Chilean deposit is a relative newcomer. The first reference to Chilean lapis lazuli dates back to the 19th century (Field, 1850a and b). Another early mention was made by Ignacio Domeyko (1860), a Polish immigrant and mining engineer who became the first director of the School of Mines at La Serena (about 140 km from the workings). The first detailed geologic studies of the deposit and mine workings were carried out by German geologist J. Bruggen (1921, 1926), who identified the host rock as contact-metamorphosed limestone. Lapis lazuli was officially recognized as the national gemstone of Chile in 1984. The Coquimbo Region is the only known source of lapis lazuli in Chile. Although reference is sometimes made to another Chilean deposit at Vicuna Mackenna Mountain near Antofagasta (Webster, 1994; Sofianides and Harlow, 1990), this material has been identified as dumortierite by Canut de Bon (1991). Once considered a minor or unimportant locality, with the lapis lazuli described as “at best mediocre” (Wyart et al., 1981), the Chilean deposit has produced significant quantities of attractive material in recent years. Today, Chilean lapis lazuli is exported in the rough, or incorporated into jewelry (see, e.g., figure 1), carvings, and decorative building materials by local artisans. This article will review the historical significance of lapis lazuli, and examine the geologic setting and gemological characteristics of material from Chile. LAPIS LAZULI FROM THE COQUIMBO REGION, CHILE